Intensity Correlations of a Light Beam Propagating in a Turbulent Medium

The intensity correlation function of a light beam with a very broad initial profile (in the plane-wave limit) propagating in a turbulent atmosphere is examined. The irreducible part of the correlation function I ({{r}₁}, z) I ({{r}₂}, z) is explicitly calculated in the leading order for various propagation distances z and intervals between observation points ξ = r1 – r2. For large ξ values, the result exhibits a universal decreasing power-law behavior { ^{ - 7/3}} for all propagation distances. For small ξ values, the correction does not depend on ξ: for small/large distances (weak/strong scintillation regime), it is small and increases/decreases according to a power law with increasing z. However, in the intermediate regime of moderate scintillations, it becomes of the order of unity, and our formula for the first correction becomes inapplicable.